This invention relates to a cutting-off tool of the type having a support, a relatively thin or leaf-shaped knife holder arranged datachably upon a lateral surface of the support, a cutting bit which is disposed replaceably at the front end of the knife holder in a V-shaped groove, and a relatively thin or leaf-shaped clamping plate movable against the knife holder in its longitudinal direction, the clamping plate being supported by the action of a set screw with its front end disposed upon the upper side of the cutting tool and being supported with its posterior end upon the knife holder.
This well known type of a cutting-off tool is not practical because experience has shown that even gentle pressing of the clamping plate upon the upper surface of the cutting bit at relatively low lateral pressure upon the clamping plate or the thin knife holder causes them to deform in such a way that the cutting bit jumps out of the V-shaped bearing groove of the knife holder. This construction is completely unsuitable for practical use because during the use of such cutting-off tools the chips which have been removed, and which are distributed within the recessed grooves, and also because of unavoidable motions of the workpiece, both subject the cutting bit to such lateral pressures that are by far larger than needed to deform the clamping plate or the knife holder so that the cutting bit jumps out of the groove.
Traditionally such difficulties were heretofore alleviated by forming a narrow, long rod and by soldering or otherwise securing the cutting bit to a respective extension part. The length of this rod was chosen to be longer than the length of the superior clamping plate so that it was possible to solidly clamp the cutting bit. This technique also served to counteract the thrust or backpressure of the cutting action against the cutting bit.
The disadvantages of the latter construction are the wasted amount of time needed for the soldering and also the waste of material required for the longitudinal, elongated cutting bit. Additionally it may be noted, that in this construction the bevel which serves to reject the chips is situated close to the upper part of the clamp. Thus the anterior edge of the clamp may be easily damaged by the chips eventually leading to imperfect fastening of the cutting bit after prolonged use. That would lead to a premature replacement of the upper clamping plate, thus again increasing the cost of the arrangement.
Accordingly, an object of the present invention is to overcome the disadvantage of these known prior art arrangements and to provide a cutting-off tool which guarantees an absolutely rigid locking of the cutting bit even under the most unfavorable working conditions and which allows an exchange of the cutting bit with as little effort as possible, thereby generally obviating repairs.
The present invention achieves this objective by shaping the cutting bit prismatically upon the upper plane which acts upon and engages the clamping plate, such prismatic surface mating with a respective V-shaped bearing groove, and by providing that the cutting bit is braced against the backpressure or thrust of the cutting by a thrust block which is solidly connected to the clamping plate. It has been found that this prismatic construction of the cutting bit solidly locks the cutting bit onto the cutting-off tool at minimal clamping pressure. This locking action prevents the cutting bit from jumping out of its holder even when very strong lateral forces impinge upon the whole tool, or when the tool is completely bent out of shape.
In a further embodiment of the present invention the clamping plate is provided with a support which is capable of being secured to the clamping plate by the thrust of a screw whereby it is furthermore extremely advantageous that the clamping plate and the knife holder bear respectively at their posterior ends against mating serrations whereby the clamping plate may be solidly locked in predetermined positions relative to the knife holder.
In a further embodiment of the present invention the clamping plate may be protected against the removed chips by providing a rejecting bevel between the working part of the cutting bit and the fastened part of the cutting bit.
The angle of the bearing prisms of the cutting bit and the V-shaped holding grooves or bearing grooves may be preferably 90.degree.. The choice of a 90.degree. angle simplifies the manufacture considerably. A considerable problem encountered with cutting-off tools and other tools such as grooving tools using cutting bits is that a satisfactory discharge of chips cannot be assured at cutting depths of more than 15 mm (5/8 inch). The jamming of chips in the indented groove impedes further cutting. Thus, hitherto existing tools were only capable of cutting deep and narrow grooves with great difficulties. This problem is even more annoying than the difficulties engendered with the mounting or fastening of the cutting bit.
Accordingly, in a further embodiment of the present invention the chips are actively shaped in such a way that they leave the groove easily so that the difficulties of the mounting or fastening of the cutting bit as regards the reaching of greater groove depths may be counteracted. This may be advantageously effected by grinding into the cutting surface of the cutting bit which serves as the guiding surface for the chips, a longitudinal groove which extends from the front edge or plane and which leads steplessly towards the rear of the guiding surface. This longitudinal groove is cut into hard metal (carbide) cutting bits with a diamond wheel and into high speed bits with a Borazon (boride) wheel. The longitudinal groove breaks the chip which was cut off the workpiece with the cutting bit into three parts according to the specific material and also according to a function of the chip angle of the cutting bit. The longitudinal groove may also shape the chip in such a way that the chip contracts, thus becoming narrower than the width of the groove. In any case the chip becomes narrower than the groove so that the chip or the several narrower parts of said chip may easily drop or pass out of the groove.
According to another embodiment of the present invention the longitudinal groove prepared by grinding may vary in diameter, and provision may be made so that the cutting plane and the bottom of the longitudinal groove exhibit different angles of chipping, preferably in such a way that the bottom of the longitudinal groove is concavely shaped in concordance with the rounding of the grinding wheel which was used to make the groove.
A cutting-off tool is already well known where near to its cutting edge a spherical indentation prepared by a sintering process is provided but such a construction of a cutting-off tool does not allow adaptability or accommodation to various working conditions so that the depth, the width, and the angle of chipping of this indentation might cause a crumbling of the removed chip or at least a shrinking of the chip. Particularly such merely spherical indentation is not capable of guiding the chips like the heretofore described longitudinal groove, a fact which is of great importance for neat guiding of chips, free of jamming, when large depths of recesses are desired. Here it should also be mentioned that cutting bits with spherical indentations, in contradistinction to the workpieces of the present invention, cannot be sharpened by grinding, and they must be thrown away once the cutting edges become dull.